Method of preventing offsetting of



Sept. 28, 1937.

R. BLOW METHOD OF PREVENTING OFFSETTING OF FRESHLY PRINTED SURFACES Filed Jan. 17, 1956 2 Sheets-Sheet l Sept. 28, 1937. R. BLOW 2,093,995

METHOD OF PREVENTING OFFSETTING OF FRESHLY PRINTED SURFACES Filed Jan.17, 1936 2 Sheets-Sheet 2 J92 fln 20 7": 267207 61 32 0 a0:

Patented Sept. 28, 1937 UNITED s'm'rizs METHOD OF PREVENTING OFFSETTINGOF FRESHLY PRINTED SURFACES Richard Blow, Chicago, Ill., assignorto W.F.

Hall Printing Company, Chicago, 111., a corporation of IllinoisApplication January 17, 1936, Serial No. 59,519

4 Claims.

This invention relates to improvements in a method of preventing theoffsetting of freshly applied ink from a recently printed sheet to asheet deposited upon said freshly printed surface.

In the printing art it is customary in the printing operation to pilefreshly printed sheets one on top of the other in the form of a stack.In view of the fact that the printed sheets are deposited in rapidsuccession on said stack, provision is usually necessary for preventingthe offsetting of the wet ink from the printed surface to the rear faceof the adjacent sheet in the stack.

Numerous expedients have been heretofore used to accomplish this endincluding the employment of a slip sheet, that is, the insertion ordeposition of a slip sheet or protector sheet between adjacent printedsheets. This expedient is satisfactory in some cases but in others it isnot effective and in all cases it is expensive, involving the cost ofthe separate mechanism required to handle the slip sheets as well as theadditional cost of the slip sheets themselves.

It has also been heretofore proposed to use wax as a protecting agent toprevent offset, said wax being sprayed onto the freshly printed surfaceof a sheet or web. This method of preventing offset althoughindifferently effective in some instances is open to the objection thatthe wax, in general, is difficult to handle. When using wax for thispurpose, the spray heads periodically clog, and all equipment adjacentthe spray becomes covered with the wax. In addition, in printingmulti-colored work, difficulty is encountered in printing subsequentlyapplied colors due 5 being printed).

to the presence of the wax upon the previously printed sheet or web.

Another commonly used expedient is the employment of an aqueoussuspension, solution or emulsion of gums or like material, which isblown upon the surface of the freshly printed sheet in the form of amist whereby said gums are deposited upon the freshly printed surfaceand serve to protect said inked surface from injurious contact with thenext adjacent sheet.

This method is open to numerous objections among which may be mentionedthe difliculty of clogging or gumming of the equipment used; and thedanger of wetting the freshly printed sheet whereby the same adheres tothe sheet deposited thereon (this diiilculty is frequently encounteredbecause of the presence of an aqueous carrier especially when coated orsemi-coated papers are Moreover, the sheets or printed web may stick oradhere due to the presence of an excess of the spray materialparticularly when a siccative material such as glue, gum arabic, or thelike is used.

In my present invention a process is described which is characterized inthat no expensive slip ,sheets are necessary and the protecting agent isbe discharged, nor in keeping the equipment free and operative over longperiods of time.

Briefly described my invention comprises periodically discharging apredetermined quantity of substantially dry, finely divided solidmaterial in company with a gaseous carrier, preferably air,

at a predetermined pressure whereby the finely divided solid material isuniformly distributed upon the freshly printed surface, protecting thatsurface from injurious contact with a superposed sheet.

The objects and advantages of my invention will be apparent from theaccompanying drawings and following detailed description.

In the drawings, Fig. 1 is a diagrammatic side elevational view of thedischarge end of a printing press illustrating suitable apparatus forcarrying out my invention.

Fig. 2 is a similar view showing the printed sheet in the act of beingdischarged.

Fig. 3, is a similar view of a modified apparatus for carrying out myinvention at a different period of travel of the printed sheet.

Fig. 4 is a side sectional view of the preliminary dusting or cloudingchamber.

Referring in detail to the drawings, (Fig. 1), l indicates the rear ordischarge end of a conventional type printing press. that my inventiondoes not appertain to the printing operation itself only the frame 2 ofthe printing press per se is illustrated.

After the printing operation is performed in the printing mechanism ofthe press, the freshly printed sheets 3 are delivered in seriatim to aconveyor which usually comprises a plurality of parallel moving conveyorbelts 4 which travel in endless fashion-around pulleys 5 in thedirection indicated by the arrows in Fig. l. The conveyor is carried byframe 6 which, in turn, is supported by legs or columns 1.

From the conveyor the sheets 3 are passed to a table 8 having supports9, said table being disposed adjacent the rear or discharge end of Inview of the fact 4 the conveyor. The sheets 3 discharged to table 3 arepiled thereon in the form of a stack III, the sheets being positioned insuperimposed re lationship. Although different type presses dischargetheprinted sheets in diflerent fashions, substantially all of thedischarge mechanisms ultimately stack the sheets, and accordingly, inview of the fact that my invention is adapted to protect the freshly,printed surfaces and prevent oflsetting when the sheets are stacked, itis applicable to substantially all types of presses.

It is to be understood, of course, that although my invention isdescribed in conjunction with, and in the environment of a press of theflatbed type. it is equally applicable to presses of the rotary typewherein the printed web is rolled or otherwise handled as a continuousweb. My invention is broadly directed to a process of preventingoffsetting of print and, consequently, is not concerned with, and theoperation thereof is not affected, by the manner in which the print isoriginally produced.

In carrying out my invention one or more guns or discharge nozzles IIare mounted upon the rear end of the frame 6, being carried by anysuitable support I2. The gun or guns II mounted in this manner are sodisposed as to discharge the protecting agent over the surface of theuppermost sheet 3 in the stack I0.

A container I3, shown in detail in Fig. 4, is positioned adjacent theconveyor frame and is connected to a source of air under pressure bymeans of a flexible conduit I4. The air delivered through conduit I4 isinitially obtained from a source of air under pressure (not shown) whichmay comprise a compressor or blower which may discharge through conduitI5. The pressure in conduit I5 is preferably higher than that adapted tobe used and, consequently, a conventional pressure regulator I6 isconnected to said conduit. A valve I1 is connected between the pressureregulator and conduit I4 and controls the passage of air through saidconduit.

As has been hereinbefore described, conduit I4 connects into containerI3, said conduit connecting into the block I8 mounted upon the cover I9of the container. A recess 20 is provided in the block I8 and a needlevalve 2| controls the passage of air from conduit I4 through recess 20,the needle valve 2| being provided with a knurled head 22 whereby thesame may be manipulated. A rotor 23 mounted upon shaft 24 may dependfrom cover I9 into the interior of container I3, shaft 24 being providedwith a recess or bore 25 which may comprise a continuation of the recess20. Rotor 23 may be substantially cylindrical in construction and isadapted to rotate upon shaft 24. Rotor 23 is provided with a pluralityof radially extending bores 26 which discharge at the exterior orperipheral surface of the rotor 23. The bore 25 in shaft 24 connectswith a bore 21 in rotor 23, said latter bore being also in communicationwith the bores 26. The bores 26 are so constructed that when air underpressure is passed from conduit I4 to the rotor bores, the rotor isrevolved by the reaction of the air being discharged at the periphery ofthe rotor.

Container I3 is adapted to carry a quantity of finely divided material33, hereinafter referred to as protecting agent. Clamps 3| may beswingably mounted upon the walls of container I3,

'said clamps being U-shaped and being adapted to extend over the coverI3 when the cover is in closure position. Screws 32 having slotted heads(not shown) are threaded into the arms of clamps 3| and are adapted tobear, at their lower ends, upon cover I9. Winged nuts 33 threadedlyengage screws 32.

Block I8 may also be provided with a bore 34 which is in communicationwith conduit I4. A flexible conduit 35 connects with bore 34 at one endand is connected at the opposite end to the gun or nozzle II. A conduit36 also connected to the gun or nozzle II connects into the top of thecontainer I3, said conduit terminating within the interior of thecontainer I3 in fitting 31.

The arrangement is such that when valve I1 is opened, air under pressurepasses through conduit I4 to block I3. Here the air stream is divided, aportion passing through bore 34 and conduit 35 to the gun II and aportion being passed downwardly through bores 20 and 25 to the interiorof the rotor 23. The air discharged from the bores 26 in rotor 23 causesaid rotor to rotate. A portion of the air is discharged from the bottomof the rotor through conduits 28 and 29, and said air stream thusdischarged impinges upon upper surface of the protecting agent '30within container I3 and agitates the same. As a consequence, a quantityof the protecting agent is thrown upwardly into the atmosphere above thebulk supply 30 and the space within the container above the bulk supply30 carries a cloud of finely divided protecting agent in suspension inthe air. As the air is discharged through conduit 35 and out of the gunII, the suspended finely divided protecting agent is also I passedthrough the conduit 36' and discharged in company with the air fromnozzle II. In this manner finely divided protecting agent is dischargedin an air suspension upon the uppermost sheet 3 of the stack III.

Valve I1 may be of the conventional solenoid operated type and thesolenoid may be connected by means of leads 33 to a switch 39 which maybe carried upon a portion of the printing press. Switch 33 is not shownin Fig. 1 but the same may be positioned at any portion of-the printingpress and may be actuated to periodically open valve I1 in timedrelation with the passage of printed sheets so that when the printedsheet 3 is discharged upon the stack I3, valve I! will be opened for apredetermined period of time suflicient to discharge a proper amount ofprotecting agent upon the freshly printed surface of the uppermost sheeton the stack.

As a possible manner of actuating valve H the switch 33 may be providedwith a rockable arm 40 which is normally maintained in OH position bymeans of the coil spring 4|. One of the conveyor belts 4 may carry camshaped lugs 42 which, during movement of the conveyor belt, contact arm40 and rock the same to -on position. It can readily be seen that duringthe period that either of the lugs 42 contact arm 40, the solenoid invalve I! will be energized to open said valve and permit air to bedischarged into the container I3 whereby protecting agent is dischargedfrom the nozzle II.

As has been hereinbefore pointed out the protecting agent comprises afinely divided solid material which is preferably of a size in theneigh- 3. This cloud, if the material is of small particle size,gradually settles upon the freshly printed tecting agent issubstantially the same.

surface of the uppermost sheet in the stack III uniformly distributingthe particles over the freshly printed surface. However, if theparticles are relatively large, or it is not desired to form the cloudabove the printed sheet or web, the material may be directly dischargedupon the printed surface. This latter procedure is particularlypreferable when the process is used with continuously passing webs as inthe case of rotary presses.

My process may be so operated, by properly timing the passage of printedsheets to the table 8 and corelating said passage with the discharge ofthe nozzle I i that a freshly printed sheet 3 may be discharged upon thestack in while the cloud of protecting agent still hovers above theuppermost sheet of the stack ID. This period of operation is illustratedin Fig. 2 and it will be observed that the sheet 3 upon the conveyor 4is being projected over the cloud 3 which has not had time to completelysettle upon the sheet 3 at the top of the stack l0. Consequently theprotecting agent comprising the cloud 43 will be trapped beneath theadvancing sheet 3 and the uppermost sheet 3 in the stack i0, therebypermitting of exceedingly rapid discharge of the sheets 3. In otherwords, the printing press may be operated at an exceedingly rapid rateand yet a suitable quantity of protecting agent will be uniformlydistributed on the freshly printed surface of each sheet.

Referring particularly to Fig. 3 a different positioning of nozzle I Iis illustrated. In this manner of carrying out my invention the nozzlell discharges while the sheet 3 is on the conveyor and before it isdeposited upon the table 8. In

other words, my invention contemplates distributing the protecting agentupon the freshly printed sheet either when it is finally positioned uponthe stack l0 and is stationary, or while it is moving. In either casethe action of the pro- Obviously the period of discharge of the nozzle Hin each case must be corelated so as to discharge a suitable quantity ofprotecting agent upon the printed surface at the proper time. In thecase of continuous web operation the nozze is so controlled as tooperate continuously.

The proportion of protecting agent discharged from the nozzle il may beregulated by the needle valve 2|. It can readily be seen that the streamof air passed through conduit I4 is divided within the block I8, aportion of said air being passed through conduit 35 and a portion beingintroduced into the interior of the container l3. If the needle valve 2|is so manipulated as to restrict the bore 20', the proportion of air toprotecting agent will be increased. If the needle valve 2| is somanipulated as to offer no obstruction to the air passing through thebore 20, the proportion of protecting agent to air will be relativelyincreased.

The protecting agent employed in comprises in general any finely dividterial which has no detrimental effect upon the printed sheet, that is,the ink, the paper or the printing quality. Moreover, it is desirablethat the material be substantially inert and noncorrosive. The particlesize of the material is smaller than approximately 75 mesh and ispreferably such as will pass a 325 mesh screen. Many materials may beused as protecting agent such as, clay or other minerals, calciumcarbonate, aluminum hydrate, French chalk, barium sulphate, titaniumoxides, calcium and magnesium sulphate, magnesium carbonate, whiting,barytes, barium sulphate, blanc fixe, lithopone, zinc oxide, zinesulphide, ponouth, Beckton white, china clay, talc and all inertsilicates. Preferably, a mixture of approximately equal parts ofprecipitated calcium carbonate and starch is employed. Precipitatedcalcium carbonate or French chalk has a relatively low specific gravityand is also deficient in covering power, that is, it is less opaque. Ifdesired, whiting may be substituted for the precipitated calciumcarbonate. Of course, other materials may be used such as substantiallyall starches, for instance, those morphologically classified in the riceor potato group. Generally, those materials which are characterized bylack of covering power, that is, relatively transparent or translucentmaterials; inertness; having properties of specific gravity, particlesize, etc., making their blowing feasible; and, of sumciently largeparticle size as to effectively serve as a protecting agent.

When using the agitating arrangement shown and described an air pressureon the gun ll of less than 25 pounds per square inch is desirable, thepressure preferably ranging in the neighborhood of five pounds persquare inch but not materially less than two pounds per square inch. Ifmechanical agitation of the agent in the initial mixing container isused, that is, if revolving .blades or the like are used to agitate thematerial 30, pressures higher than twenty-five pounds per square inchmay be used.

It is to be understood, of course, that although the protecting agent isshown and described as being discharged downwardly upon the freshlyinked surface, the discharge may be in an upwardly direction, that is,the sheet or web may be delivered or traveling with its printed facedownwardly or the discharge may be made while the web or sheet istraveling vertical.

I claim as my invention:

1. A method of preventing offsetting of ink from a freshly printed sheetwhich comprises, maintaining a quantity of dry, finely dividedprotecting agent in an enclosed zone, introducing air under pressure tosaid enclosed zone to agitate said protecting agent and form a cloud ofprotecting agent suspended in air in said zone, passing said suspendedprotecting agent to a discharge, simultaneously passing airunimpregnated with suspending agent and under pressure through saiddischarge to serve as a carrier for said suspended protecting agent, anddischarging said air-carried suspended protecting agent on to a freelyprinted surface.

2. A method of preventing offsetting of ink from a freshly printed sheetwhich comprises, maintaining a quantity of dry, finely dividedprotecting agent in an enclosec. zone, introducing air under pressure tosaid enclosed zone, dividing said air and passing a portion thereof intosaid enclosed zone to agitate said protecting agent and form a cloud ofprotecting agent suspended in the air in said zone, discharging saidprotecting agent from said zone to the surface of a freshly printedsheet, and simultaneously discharging the remainder of the air passed tosaid zone in company with said suspended protecting agent to serve as acarrier therefor. I

3. A method of preventing offsetting of ink from stacked freshly printedsheets which comprises, maintaining a quantity of dry finely dividedprotecting agent in an enclosed zone, passing air under a pressuregreater than two pounds per square inch and preferably less than prises,maintaining a quantity of dry finely' divided protecting agent of aparticle size smaller than 75 mesh and preferably in the neighborhood of325 mesh in an enclosed zone, passing air under a pressure greater thantwo pounds per square inch and preferably less than twenty-five poundsper square inch to said zone. dividing said air and passing a portionthereof into said enclosed zone to agitate said protecting agent andform a cloud of protecting agent suspended in the air in said enclosedzone. discharging. said protecting agent from said zone to the surfaceof a freshly printed sheet, and simultaneously discharging the remainderof the air passed to said zone in company with said suspended protectingagent to serve as a carrier therefor.

RICHARD BLOW.

